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Chronology and orientation of N2–CH4, CO2-H2O, and H2O-rich fluid-inclusion trails in intrametamorphic quartz veins from the Cuiabá gold district, Brazil

Published online by Cambridge University Press:  05 July 2018

C. J. S. de Alvarenga ,
M. Cathelineau  and
J. Dubessy
C. J. S. de Alvarenga
Affiliation:
Departamento de Geologia, Universidade Fed. de Mato Grosso, Cuiabá, 78100, Brazil
M. Cathelineau
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54500, Vandoeuvre-les-Nancy, France
J. Dubessy
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54500, Vandoeuvre-les-Nancy, France
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Abstract

The upper Proterozoic Cuiabá group of Mato Grosso, Brazil, is composed of low-grade clastic meta-sediments which have been folded by several successive tectonic events. Three generations of quartz veins are associated with the structural evolution of this area. The first veins are deformed by the main tectonic phases and show a complex deformational patterns. The second set is parallel to the cleavage and was formed syntectonically during the main folding phase, whilst the last quartz veins are related to a later stage of deformation. A systematic study of fluid inclusions in relation with a statistical study of microstructural markers (fluid inclusion trails, opened microcracks) was carried out on quartz veins from three localities. On the basis of microthermometric studies and Raman spectrometry analysis, four differents types of fluids have been distinguished, each trapped in specific fluid inclusion trails: (i) CO2-rich liquids and vapours (Lc, Vc) at Casa de Pedra, (ii) Lc and Vc inclusions with variable amounts of CO2, CH4, N2 in the vapour phase at BR-70, (iii) CH2-N2-rich vapours (Vn-m), and (iv) aqueous inclusions (L) with variable salinities representing the last fluid generations at all localities.

At Casa de Pedra and BR-70, most fluids are observed within the three generations of quartz veins, indicating an important fluid circulation associated with the last phase of brittle deformation. Fluid inclusions of type (iii) and (iv) are oriented along several well defined directions. The study shows the importance of integrated microstructural and fluid-inclusion studies for understanding the geometry and chronology of fluid circulation.

Keywords

fluid-inclusion trailsquartz veinsgoldBrazil
Type
Ore environments—gold mineralization
Information
Mineralogical Magazine , Volume 54 , Issue 375 , June 1990 , pp. 245 - 255
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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Footnotes

*

Present address: Lab. de Géologie Dynamique et Petrologie de la Surface, Centre de St. Jérôme, 13397 Marseille, France.

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